The invention relates to a thread control device for a chainstitch sewing machine of the type including a rotatably mounted shaft, a reciprocating needle bar having a stitching needle including an eye through which the stitching thread is threaded, drive means connecting said rotatably mounted shaft to said reciprocating needle bar, a thread tensioning device and a thread feeder including a thread-guiding orifice.
A thread control device of this general type is disclosed in U.S. Pat. No. 3,460,494. In this prior art thread control device a guide eyelet, which serves to draw off or feed the thread, is attached to the needle bar. The stitching thread is threaded through the guide eyelet. A thread feeder of this type serves in a known manner in chainstitch sewing machines during the switch-forming procedure to both draw off a quantity of thread, from the thread supply, necessary to form the stitch and also to tighten the loose stitching thread required to form the needle thread loop.
Although the prior art thread feeder, which guides the thread and is connected to the needle bar, renders it possible for the parts to have a simple design, it does not allow any fine adjustments of the thread control device to suit the quantity of thread required during the individual phases of the stitch formation procedure. Furthermore, the total weight of the needle bar is increased owing to the thread feeder being fixedly attached to the needle bar. As a consequence the mass forces acting upon the needle bar drive are increased. This can cause premature wear of the sewing machine.